Functionalized superhydrophobic melamine sponge and preparation method and application thereof

Abstract

This invention relates to the field of materials technology for treating oily wastewater, specifically disclosing a functionalized superhydrophobic melamine sponge, its preparation method, and its applications. Using melamine sponge as a matrix, stearic acid-grafted attapulgite (grafting rate of 15-25%) and polydimethylsiloxane are synergistically loaded onto the surface of a micron-scale framework-nanoparticle multi-level structure through silanization modification, amidation grafting, and dip-coating curing processes. The grafted attapulgite fundamentally imparts hydrophobicity to the nanoparticles and firmly binds them to PDMS. The optimal water contact angle is ≥159°, the adsorption capacity for oils such as palm oil reaches up to 112.3 g / g, and the oil-water mixture separation efficiency exceeds 98%. The sponge retains its hydrophobicity after 40 mechanical abrasion cycles, exhibits stable performance in acidic / alkaline environments of pH 2-12, and retains over 89.7% of its capacity after 20 adsorption-extrusion cycles, providing a new solution for efficient and durable oil-water separation materials.

Description

Technical Field

[0001] This invention relates to the field of materials technology for treating oily wastewater, and specifically discloses a functionalized superhydrophobic melamine sponge, its preparation method, and its application. Background Technology

[0002] With the rapid development of industries such as petrochemicals, shipping, and food processing, oily wastewater (industrial discharges, oil spills, food processing wastewater, etc.) poses a serious threat to the ecological environment and human health. Developing efficient, economical, and environmentally friendly oil-water separation materials is currently a research hotspot. Traditional oil-water separation materials, such as activated carbon and expanded graphite, suffer from problems such as low adsorption capacity, poor selectivity, and unsatisfactory recycling performance. Melamine foam (MS) has become an ideal substrate due to its three-dimensional porous structure, high porosity, and good elasticity. However, the original MS is amphiphilic (both hydrophilic and oleophilic), lacking oil-water selectivity, which limits its application in the field of oil-water separation.

[0003] Existing techniques typically involve surface hydrophobic modification of MS to impart superhydrophobic / superoleophilic properties. Common modification strategies include: 1) loading low surface energy materials (such as polydimethylsiloxane (PDMS) or fluorinated reagents); 2) constructing micro / nano rough structures (such as loading SiO2, graphene, or other nanoparticles).

[0004] CN119751969A modifies MS using a composite silane coupling agent (MTS / APTES) and nano-SiO2, but its adsorption capacity and separation efficiency for high-viscosity oils need improvement. CN111073031A utilizes graphite particles unfolded within a polymer monomer to form graphene nanosheets, which are then fixed onto MS via polymerization crosslinking; however, the process involves emulsion polymerization, making the steps relatively cumbersome. CN120420957A modifies MS using a covalent organic framework (COF), achieving excellent performance, but the high cost and complex synthesis of COF monomers hinder large-scale application. CN119701894A uses natural urushiol and Fe3O4 to impart hydrophobicity and magnetism to MS, but this relies primarily on physical coating, potentially limiting the binding force and long-term stability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a superhydrophobic melamine sponge with high adsorption capacity, good selectivity, excellent stability, simple preparation process and low raw material cost, as well as its preparation method and application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The functionalized superhydrophobic melamine sponge is based on melamine sponge and loaded with a composite functional coating. The composite functional coating includes polydimethylsiloxane and stearic acid-grafted attapulgite nanoparticles. The grafting rate of stearic acid in the stearic acid-grafted attapulgite nanoparticles is 15% to 25%. Preferably, the grafting rate of stearic acid in the stearic acid-grafted attapulgite nanoparticles is 20% to 21%.

[0008] The resulting superhydrophobic melamine sponge has a water contact angle of ≥150°, exhibiting superhydrophobic / superoleophilic properties, providing a structural basis for efficient oil-water separation.

[0009] This invention also provides a method for preparing functionalized superhydrophobic melamine sponge, comprising the following steps:

[0010] S1. Preparation of stearic acid-grafted attapulgite nanoparticles: Acidified attapulgite was modified by silanization with γ-aminopropyltriethoxysilane (KH-550) to obtain aminated attapulgite; then aminated attapulgite and stearic acid were subjected to amidation reaction in the presence of condensing agents 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) to obtain stearic acid-grafted attapulgite nanoparticles.

[0011] In step S1, γ-aminopropyltriethoxysilane (KH-550) can efficiently introduce amino active sites, laying the foundation for subsequent amidation grafting.

[0012] Setting the molar ratio of stearic acid (SA): 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC): N-hydroxysuccinimide (NHS) = 1:1.2:1.2 can promote the efficient reaction between the carboxyl group of stearic acid and the amino group of aminated attapulgite, achieve a firm grafting of stearic acid, and fundamentally change the hydrophilicity of attapulgite to make it hydrophobic.

[0013] S2. Preparation of dipping coating solution: Mix polydimethylsiloxane prepolymer and curing agent at a mass ratio of 10:1, dissolve in the organic solvent isopropanol, add stearic acid-grafted attapulgite nanoparticles, and ultrasonically disperse evenly to obtain the dipping coating solution.

[0014] In step S2, the concentration of polydimethylsiloxane in the dipping solution is preferably 20~40 mg / mL, and the amount of stearic acid-grafted attapulgite nanoparticles added is 0.2%~0.7% of the total mass of the dipping solution.

[0015] S3. Loading and curing: The pretreated (cleaned and dried) melamine sponge is immersed in the immersion coating solution. After vacuum immersion for 0.5 hours and atmospheric pressure immersion for 1.5 hours, it is taken out, excess liquid is squeezed out, and it is cured at 70~80℃ for 6~10 hours to obtain a superhydrophobic sponge.

[0016] The superhydrophobic melamine sponge prepared by the present invention is used for oil-water separation, specifically for separating oil-water mixtures, oil-in-water emulsions, and treating oily wastewater. It can be widely used in oily wastewater treatment and oil spill emergency response in the fields of petrochemicals, shipping, and food processing.

[0017] Beneficial effects:

[0018] (1) Stearic acid-grafted attapulgite nanoparticles were combined with PDMS for the modification of melamine sponges. The long alkyl chain of stearic acid was firmly grafted onto attapulgite through chemical bonds, fundamentally changing the hydrophilicity of ATP and making it a stable hydrophobic nanounit. This hydrophobic nanounit, in synergy with the PDMS polymer network, constructed a unique "micron framework-nanoparticle" multi-level rough structure on the MS framework, which is the key to achieving superhydrophobicity and high adsorption capacity. The adsorption capacity for relatively viscous oils such as palm oil reached up to 112.3 g / g, far exceeding that of traditional materials; the separation efficiency of oil-water mixtures under gravity drive was >98%, which can effectively separate oil-in-water emulsions; excellent stability: it still maintains high hydrophobicity after 40 mechanical abrasions; it is stable in a wide range of acid and alkaline environments with pH=2~12; the capacity retention rate after 20 adsorption-extrusion cycles was >89.7%;

[0019] (2) The preparation process of this invention is simple, the conditions are mild, and no complicated equipment is required. The main raw materials (attapulgite clay, stearic acid, PDMS, and melamine sponge) are all cheap and readily available industrial products, with low cost and easy to scale up production. This material provides a new, efficient, economical, and environmentally friendly solution to the problem of treating oily wastewater, and has great practical application value in the fields of petrochemicals, shipping, and food processing. Attached Figure Description

[0020] Figure 1 The image shows the FT-IR spectrum of stearic acid-grafted attapulgite nanoparticles (SA-g-OATP) prepared in Example 1 of this invention.

[0021] Figure 2 The images show a comparison of the microstructure of stearic acid-grafted attapulgite nanoparticles (SA-g-OATP) prepared in Example 1 of this invention with that of the original ATP (top image, ATP (left), SA-g-OATP (right)), as well as a comparison of their dispersibility in polar (water) and non-polar (isopropanol) solvents (middle image, isopropanol (left), water (right)) and water contact angle (bottom image, ATP (left), SA-g-OATP (right)).

[0022] Figure 3Comparison of SEM images of the microstructure of the original sponge, the superhydrophobic sponge prepared in Example 1, Comparative Example 1 and Example 2: (a) Original sponge (MS); (b) Superhydrophobic sponge prepared in Example 1 (MS1-1); (c) Comparative sample sponge prepared in Comparative Example 1 (MS1-0); (d) Superhydrophobic sponge prepared in Example 2 (MS1-3) (top); (e) EDS image of MS1-1 prepared in Example 1 (bottom).

[0023] Figure 4 The FT-IR spectra of the superhydrophobic sponge (MS1-1) prepared in Example 1 of this invention and the original MS are shown.

[0024] Figure 5 The images show the floating state of the superhydrophobic sponge prepared in Example 1 of this invention and the original sponge in water (left), the droplet behavior on the surface of the MS1-1 sponge (middle), and the water contact angle measurement diagram (right).

[0025] Figure 6 This is a bar chart showing the absorption capacity of the superhydrophobic sponge prepared in Example 1 of the present invention for different oils and organic solvents.

[0026] Figure 7 The graph shows the recycling efficiency (left) of the superhydrophobic sponge prepared in Example 1 of this invention for n-hexane / dichloromethane-water and its recycling performance (right).

[0027] Figure 8 The selective adsorption diagrams of hexane / dichloromethane-water on the superhydrophobic sponge prepared in Example 1 of this invention are shown (hexane-water (top); dichloromethane-water (bottom)).

[0028] Figure 9 The left image shows the effect of attapulgite on the superhydrophobic sponges prepared in Examples 1-3 and Comparative Examples 1-2 of this invention before and after modification (left image) and the right image shows the performance comparison of different SA-g-OATP particle contents and PDMS concentrations (right image). Detailed Implementation

[0029] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto. Unless otherwise specified, the reagents and instruments used in the embodiments are all commercially available products conventional in the art.

[0030] Example 1

[0031] Preparation of SA-g-OATP nanoparticles

[0032] 10g of attapulgite (ATP, 1250 mesh) was weighed and dispersed in 200mL of 3mol / L HCl solution. The mixture was stirred at 80℃ for 6h, centrifuged, and washed until neutral to obtain acidified ATP (ac-ATP). The wet ac-ATP was redispersed in a mixture of 90mL anhydrous ethanol and 10mL deionized water. 2mL of γ-aminopropyltriethoxysilane (KH-550) was added, and the pH was adjusted to 4-5 with glacial acetic acid. The reaction was carried out at 70℃ for 4h to obtain aminated attapulgite (OATP). Subsequently, 4g of stearic acid (SA), 1g of EDC·HCl, and 0.6g of NHS were added to the system, and the reaction was continued at 70℃ for 5h. After the reaction, the product was repeatedly washed with anhydrous ethanol and deionized water, filtered, dried at 80℃ for 24h, and ground to obtain SA-g-OATP powder. The TGA test showed that the stearic acid grafting rate was approximately 20.73%.

[0033] Preparation of superhydrophobic sponge MS1-1

[0034] Commercial melamine sponge was cut into 2cm×2cm×2cm pieces and ultrasonically cleaned sequentially with anhydrous ethanol and deionized water for 10 min each, then dried at 60℃. 1g of PDMS prepolymer (Sylgard 184 component A) was weighed and mixed with 0.1g of curing agent (component B), then added to 50mL of isopropanol and magnetically stirred to dissolve, preparing a PDMS solution with a concentration of 20 mg / mL. 0.11g of SA-g-OATP powder (0.22% of the total solution mass) was added to this solution, and the mixture was magnetically stirred and ultrasonically dispersed for 1 h to obtain a uniform coating solution. The pretreated sponge was immersed in the coating solution and placed in a vacuum desiccator for 0.5 h at -0.1 MPa, followed by 1.5 h at normal pressure. The sponge was removed, and excess liquid was gently squeezed off the surface. It was then cured in a 70℃ oven for 8 h to obtain a superhydrophobic sponge, denoted as MS1-1.

[0035] Comparative Example 1

[0036] Commercial melamine sponge was cut into 2cm×2cm×2cm pieces, and ultrasonically cleaned sequentially with anhydrous ethanol and deionized water for 10 min each, then dried at 60℃. 1g of PDMS prepolymer (Sylgard 184 component A) was weighed and mixed with 0.1g of curing agent (component B), then added to 50mL of isopropanol and magnetically stirred to dissolve, preparing a PDMS solution with a concentration of 20 mg / mL (without adding SA-g-OATP powder), resulting in a uniform coating solution. The pretreated sponge was immersed in the coating solution and placed in a vacuum desiccator at -0.1MPa for 0.5h, followed by immersion at normal pressure for 1.5h. The sponge was removed, and excess liquid was gently squeezed off the surface. It was then cured in a 70℃ oven for 8h to obtain a superhydrophobic sponge, denoted as MS1-0.

[0037] Comparative Example 2

[0038] Commercial melamine sponges were cut into 2cm×2cm×2cm pieces and ultrasonically cleaned sequentially with anhydrous ethanol and deionized water for 10 min each, then dried at 60℃. 1g of PDMS prepolymer (Sylgard 184 component A) was weighed and mixed with 0.1g of curing agent (component B), then added to 50mL of isopropanol and magnetically stirred to dissolve, preparing a PDMS solution with a concentration of 20 mg / mL. 0.11g of ATP or OATP powder (0.22% of the total solution mass) was added to this solution, and the mixture was magnetically stirred and ultrasonically dispersed for 1 h to obtain a uniform coating solution. The pretreated sponges were immersed in the corresponding coating solutions and placed in a vacuum desiccator at -0.1MPa for 0.5 h, followed by immersion at normal pressure for 1.5 h. The sponges were then removed, gently squeezed to remove excess liquid from the surface, and cured in a 70℃ oven for 8 h to obtain superhydrophobic sponges, denoted as ATP / PDMS@MS and OATP / PDMS@MS.

[0039] Example 2: Preparation of sponges with different amounts of SA-g-OATP

[0040] The preparation steps for SA-g-OATP powder are the same as in Example 1.

[0041] Commercial melamine sponges were cut into 2cm×2cm×2cm pieces and ultrasonically cleaned sequentially with anhydrous ethanol and deionized water for 10 minutes each, then dried at 60℃. 1g of PDMS prepolymer (Sylgard 184 component A) was weighed and mixed with 0.1g of curing agent (component B), then added to 50mL of isopropanol and magnetically stirred to dissolve, preparing a PDMS solution with a concentration of 20 mg / mL. 0.22g and 0.33g of SA-g-OATP powder (corresponding to 0.44% and 0.66% of the total mass of the coating solution, respectively) were added to this solution, magnetically stirred, and ultrasonically dispersed for 1 hour to obtain a uniform coating solution. The pretreated sponges were immersed in the coating solution and placed in a vacuum desiccator at -0.1MPa for 0.5 hours, followed by immersion at atmospheric pressure for 1.5 hours. Remove the sponge, gently squeeze to remove excess liquid from the surface, and place it in a 70℃ oven to cure for 8 hours to obtain the corresponding superhydrophobic sponges, denoted as MS1-2 and MS1-3.

[0042] Example 3: Preparation of sponges with different PDMS concentrations and powder amounts

[0043] The preparation steps for SA-g-OATP powder are the same as in Example 1.

[0044] Commercial melamine sponges were cut into 2cm×2cm×2cm pieces and ultrasonically cleaned sequentially with anhydrous ethanol and deionized water for 10 minutes each, then dried at 60℃. 2g of PDMS prepolymer (Sylgard 184 component A) was weighed and mixed with 0.2g of curing agent (component B), then added to 50mL of isopropanol and magnetically stirred to dissolve, preparing a PDMS solution with a concentration of 40mg / mL. 0.11g, 0.22g, and 0.33g of SA-g-OATP powder (0.22%, 0.44%, and 0.66% of the total solution mass, respectively) were added to this solution, magnetically stirred, and ultrasonically dispersed for 1 hour to obtain a uniform coating solution. The pretreated sponges were immersed in the coating solution and placed in a vacuum desiccator at -0.1MPa for 0.5 hours, followed by immersion at normal pressure for 1.5 hours. Remove the sponge, gently squeeze to remove excess liquid from the surface, and place it in a 70℃ oven to cure for 8 hours to obtain the corresponding superhydrophobic sponges, denoted as MS2-1, MS2-2, and MS2-3.

[0045] Performance Tests and Results

[0046] FT-IR ( Figure 1 SA-g-OATP at 2920cm -1 and 2850cm -1 A strong CH stretching vibration peak (stearic acid long chain) appears at 1735 cm⁻¹. -1 The presence of a characteristic peak for amide bonds confirms successful grafting.

[0047] SEM and EDS analysis ( Figure 2 , Figure 3 The original MS skeleton surface is smooth. Figure 3 a). The surface of the MS1-1 sponge skeleton is uniformly covered with a layer of granular material, forming a significant micro / nano secondary rough structure. Figure 3 b), while the surface of MS1-0 is relatively smooth ( Figure 3 c). EDS mapping shows that Si, O, and C elements are uniformly distributed on the MS1-1 framework. Figure 3 e), confirming the successful loading of the SA-g-OATP and PDMS composite coating.

[0048] Water contact angle ( Figure 5 Using a contact angle meter, the static water contact angle of the MS1-1 sponge was 159.3±1.5°, exhibiting typical superhydrophobic properties; while the original sponge had a contact angle of 0° (completely hydrophilic), and the MS1-0 contact angle was approximately 142°, indicating that the addition of SA-g-OATP improved the hydrophobicity of the sponge.

[0049] The dried sponge sample (prepared in Example 1) was immersed in various oils and organic solvents until saturation adsorption, and the adsorption capacity (g / g) was calculated by weighing. The adsorption capacities of MS1-1 sponge for palm oil, corn oil, n-hexane, and petroleum ether were 112.3, 111.87, 58.11, and 50.54 g / g, respectively. Figure 6 The efficiency was significantly higher than that of the control sample MS1-0 (PDMS modified only). For hexane / dichloromethane-water mixtures, the separation efficiency under gravity exceeded 98%. After static separation of the water-in-hexane emulsion, the emulsion became clear, and oil droplets were effectively removed under a microscope. After 40 cycles of tape peeling and sandpaper abrasion, the WCA of the MS1-1 sponge remained above 143.87° and 139.65°, respectively; after soaking in solutions with pH = 2~12 for 24 hours, the sponge's mass retention rate was >98%, and the WCA change was <8°; after 20 cycles of "adsorption-manual extrusion desorption" tests on hexane and petroleum ether, the adsorption capacity retention rate of the MS1-1 sponge exceeded 89.7%. Figure 5 ).

[0050] The above embodiments demonstrate that this invention successfully prepared highly hydrophobic and well-dispersible SA-g-OATP nanoparticles via a chemical grafting strategy, and then synergistically loaded them with PDMS onto a melamine sponge using a simple impregnation-curing process. The resulting superhydrophobic sponge (MS1-1) exhibits extremely high oil adsorption capacity, excellent oil-water selectivity and separation efficiency, as well as superior mechanical and chemical stability and recyclability. This method utilizes inexpensive and readily available raw materials, and the process is simple and environmentally friendly, providing a new technical solution for the large-scale preparation and application of highly efficient oil-water separation materials.

Claims

1. A functionalized superhydrophobic melamine sponge, characterized in that, The functionalized superhydrophobic melamine sponge is based on melamine sponge and loaded with a composite functional coating; the composite functional coating includes polydimethylsiloxane and stearic acid-grafted attapulgite nanoparticles; the grafting rate of stearic acid in the stearic acid-grafted attapulgite nanoparticles is 15%~25%.

2. The functionalized superhydrophobic melamine sponge according to claim 1, characterized in that, The stearic acid grafting rate in the stearic acid-grafted attapulgite nanoparticles is 20%~21%.

3. The functionalized superhydrophobic melamine sponge according to claim 1, characterized in that, The functionalized superhydrophobic melamine sponge has a water contact angle ≥150°.

4. A method for preparing a functionalized superhydrophobic melamine sponge according to any one of claims 1-3, characterized in that, The preparation method steps are as follows: (1) Preparation of stearic acid-grafted attapulgite nanoparticles: acid-treated attapulgite was modified by silanization to obtain aminated attapulgite; then aminated attapulgite and stearic acid were subjected to amidation reaction under the action of a condensing agent to obtain stearic acid-grafted attapulgite nanoparticles. (2) Preparation of dip coating solution: After mixing polydimethylsiloxane prepolymer and curing agent, dissolve in organic solvent, then add stearic acid-grafted attapulgite nanoparticles from step (1), disperse evenly, and obtain dip coating solution; (3) Loading and curing: The pretreated melamine sponge is immersed in the coating solution of step (2), and then cured after removal to obtain functionalized superhydrophobic melamine sponge.

5. The preparation method according to claim 4, characterized in that, In step (1), the silane coupling agent used for silanization modification is γ-aminopropyltriethoxysilane.

6. The preparation method according to claim 4, characterized in that, In step (1), the condensing agents used in the amidation reaction are 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride EDC·HCl and N-hydroxysuccinimide NHS.

7. The preparation method according to claim 4, characterized in that, In step (2), the organic solvent is isopropanol; the concentration of polydimethylsiloxane in the dipping solution is 20~40 mg / mL, and the amount of stearic acid-grafted attapulgite nanoparticles added is 0.2%~0.7% of the total mass of the dipping solution.

8. The preparation method according to claim 4, characterized in that, In step (3), the impregnation process includes vacuum impregnation and atmospheric pressure impregnation; the curing temperature is 70~80℃ and the curing time is 6~10 hours.

9. An application of the functionalized superhydrophobic melamine sponge according to any one of claims 1-3, characterized in that, The functionalized superhydrophobic melamine sponge is used for oil-water separation.

10. The application according to claim 9, characterized in that, Functionalized superhydrophobic melamine sponges are used to separate oil-water mixtures, oil-in-water emulsions, or treat oily wastewater.

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